Storage facility for the storage of highly volatile hydrocarbons

ABSTRACT

The invention relates to a storage facility for the storage of highly volatile hydrocarbons, comprising at least one vertical round tank (I) which is equipped with a floating cover ( 5 ), covering the liquid surface, in the form of a floating roof or a floating ceiling, wherein an annular space ( 8 ) formed between the cover ( 5 ) and tank wall ( 3 ) is sealed by means of flexible sealing elements ( 9 ) and wherein fittings ( 12, 13 ) for automatic control of overpressures and under pressures in the space ( 4 ) under the cover ( 5 ) are integrated into the cover ( 5 ). The fittings ( 12, 13 ) of the at least one round tank (I) are connected to a vapour line ( 14 ), the upper end of which is led out of the tank ( 1 ) and is in turn connected to a separate vapour expansion tank ( 15 ), wherein the round tank (I) and the vapour compensation tank ( 15 ) form a closed system.

BACKGROUND OF THE INVENTION

The present invention relates to a storage facility the storage of highly volatile hydrocarbons with at least one vertical round container.

The storage of highly volatile hydrocarbons in non-pressurized and aboveground storage tanks is generally done in vertical round containers with a flat bottom, which are fitted with floating covers to prevent emissions and fire risks. Large containers of this type are most often equipped as floating roof tanks without a fixed roof. Smaller storage containers as well as containers for finished products often have a fixed roof and are equipped with an internal floating cover.

Even after 100 years of development of storage concepts, these storage containers still operate under temporarily increased emissions and associated fire risks.

Storage of volatile hydrocarbons in closed containers, without a floating cover, and instead with vapor balancing and vapor recovery, which is also used, leads to a great deal of effort in the treatment of large amounts of vapor due to the daily “breathing” of the containers and is not attractive or not economical for large container volumes. Therefore, particularly in storage facilities with large individual containers, floating covers without further measures with regard to the removal of the vapors generated in the containers continue to be used.

The storage of highly volatile hydrocarbons results in multiple problems that arise with existing storage facilities.

Multiple problems result from the storage of highly volatile hydrocarbons with existing storage facilities.

The first set of problems is vapor escaping in special operating situations, the extreme heat-up of the contents of the storage containers on summer days, the unintentional introduction of air or vapors when filling the container (e.g., during ship unloading or from a pipeline), the introduction of overly warm storage products, and the pressure release of supplied storage products.

The resulting excess vapors escape from overpressure fittings and from the edge areas of the floating covers which in extreme cases can lead to lifting the cover off the stored liquid with the potential for serious damage to the storage container up to the risk of fire hazards.

A second set of problems is that the container volume cannot be completely utilized since the floating cover loses its emission-limiting effect as soon as the liquid level in the container drops below the support height of the floating cover with which the floating cover rests on the bottom of the container. At this liquid level, a safety fitting opens to protect against vacuum and prevent possible destruction of the floating cover. In this case, air from the atmosphere replaces the removed storage liquid and, when the container is subsequently filled, leads to necessary vapor emissions, which can be up to one kilogram of stored product per cubic meter of air. The loss of storage volume is, therefore, about 10% to 15%.

A third problem to be mentioned is that, in order to minimize the emissions mentioned above in the context of the second set of problems, floating roof tanks (which do not have a fixed tank roof) are in particular provided with height-adjustable float roof supports with which the floating roof is supported on the bottom of the container when the liquid level is low.

For normal operation of the container, the roof supports are moved to a higher position so that they protrude only about 1 m from the underside of the floating cover; the distance between the tank bottom and the lowest floating roof position is only about 1 m and the tank volume can be utilized better. Before planned repairs to the container, the roof supports are moved when the container is filled such that they hold the floating roof at a high position about 2 m above the bottom of the tank.

The adjustment of the floating roof supports is associated with risks for the assembly personnel as well as with fire hazards. Frequently, concentric tubes that can slide in relation to each other (leg and supporting jacket tube) are used for the floating-roof supports, which corrode and are then difficult to move. However, if additionally the tank has a fixed roof and an inner floating cover, the adjustability of the supports is often omitted, since the necessary work with a filled tank and a closed space is already too high a risk. This means that the respective floating covers are usually only equipped with fixed supports (2 m support height).

A further, fourth set of problems can be observed in the fact that the gas space under the floating cover has to be degassed after a complete emptying of the container for an intended repair. For this purpose, third-party companies are required, which extract the vapors from the dead space of the container and burn them. For larger containers, this work can take several weeks and leads to enormous costs and to safety risks. In addition, during the final combustion phase of this work, when the vapor concentration decreases, a foreign gas must be mixed before combustion, a measure that is compulsory for environmental reasons.

Another, fifth set of problems is the fact that the enormous effort involved in completely emptying the containers not only entails enormous costs and risks, but also a major hindrance for a flexible reallocation of the tank space for a possible product change. This is contrary to the present requirement that storage tanks must be designed very flexibly for modified storage needs in order to best rent the existing storage volumes.

SUMMARY OF THE INVENTION

The present invention is based on a storage facility for the storage of highly volatile hydrocarbons with at least one vertical round container, the round container being provided with a floating cover covering the liquid surface in the form of a floating roof or a floating cover; the annular space formed between the cover and the container wall is sealed by means of flexible sealing elements. Fittings for automatic control of high and low pressure in the space below the cover are integrated into the floating cover.

Based on this prior art, the problem addressed by the present invention is that of drastically reducing the above-mentioned emissions and fire risks. Furthermore, the storage space shall be made almost 100% usable and the flexibility of the storage space for product reallocation shall be increased. It shall also be possible to utilize emissions for energy.

This problem is solved by the features of claim 1. Preferred embodiments of the invention become apparent from the dependent claims.

The invention is characterized in that the fittings of the at least one round container are connected to a vapor line, which is routed out of the container at the upper edge (preferably above the upper edge of the container) and in turn is connected to a separate vapor equalization container, buffering vapors which must be supplied to or discharged from the space under the cover under certain operating conditions. The round container and the vapor equalization container form a closed system, which results in a complete separation between the atmosphere and the stored product. The fittings are used to protect the space below the floating cover against overpressure as well as against a possibly occurring vacuum.

Consequently, the above-mentioned problems do not occur or are largely avoided by the measures according to the invention.

One preferred embodiment provides that the vapor line has a vertically extending section inside the round container which is configured as a bellows and which expands or contracts depending on the floating height of the floating cover. Due to this bellows, the vapor line is lengthened or shortened according to the position of the floating cover as a result of the container fill level.

It is also provided that the bellows of the vapor line surrounds a fixed support and that the bellows is attached to the upper end of the support. The attachment point of the bellows on the support forms a fixed reference point for the bellows. The lower end of the bellows is preferably attached to a construction part of the floating roof and changes with the floating position of the floating roof.

A further advantage is achieved when the support that is surrounded by the bellows is simultaneously designed as a sampling, sounding, measuring and/or guide tube or as a roof support, as a result of which the vertical feed-through of the support is simultaneously sealed by the floating cover. The bellows is already present on some containers today, as the vertical feed-throughs through the floating cover are today the largest source of emissions at the container. In one alternative embodiment, the vapor line can be along a rolling ladder inside a round container. Such a rolling ladder is pivotally connected to the region of the upper edge of the round container while the lower end is provided with casters and rolls along a roller track resting on the floating cover. As the float height of the floating roof changes, the rolling ladder changes its inclination, whereby the casters are always guided along the roller track. The rolling ladder is thus a stable mount for the vapor line.

The vapor equalization container is preferably one with a flexible membrane with a ballast weight acting upon it. The necessary pressure in the space of the equalization container can be set via the size of the ballast weight used.

In a further embodiment, the annular space between the floating cover, the container wall and an edge seal above the liquid surface should be connected to the space below the floating cover in order to also remove vapors accumulating there from this annular space.

In particular, in order to utilize the proportion of the vapors from the round container that cannot be accommodated by the vapor equalization container or, if applicable, further collecting devices, a vapor recovery and/or vapor combustion device is connected to the vapor equalization container.

The invention is to be used preferably when the storage facility comprises a plurality of storage containers. In such a case, these storage containers are connected to a common vapor equalization container.

Taking into account the flow resistances of the vapor line, the vapor equalization container with its ballast weight should be designed to prevent a vacuum in the space below the cover by supplying vapors to this space, and should also be designed to provide a pre-specified overpressure in this space below the cover by absorbing vapors from the space.

In order to assist in discharging the vapors to the vapor equalization container, a blower can be arranged in the vapor line, which is controlled via pressure sensors in the tank container below the floating cover.

The invention also relates to a storage facility with several storage containers, these storage containers being subdivided into at least two groups, the allocation to the at least two groups being affected by the pressure exerted on the liquid by the floating cover. Each storage container of a group is assigned to a vapor equalization container adapted to this pressure. The different vapor equalization containers are connected via a vapor equalizing line into which a pressure-increasing blower is inserted for conveying vapors from the low-pressure vapor equalization container to the higher-pressure vapor equalization container. This results in a flexible and self-acting system for absorbing and buffering vapors to be discharged from the respective containers and supply them again to the inner spaces of the containers, if necessary. The system operates on the one hand through the weight of the floating cover and on the other hand through the ballast weight in the vapor equalization container autonomously.

Furthermore, it is provided that the space remaining between the floating cover and the container bottom in the lowest position of the floating cover of the round container is connected to a purging liquid reservoir and the hydrocarbon vapors present in the remaining space after the container has been emptied are discharged by introducing the purging liquid into the round container up to the support height of the floating cover to the vapor equalization container. In such a case, water or storage liquids with a low vapor pressure from other storage containers of the storage facility can be used as the purging liquid.

The storage facility according to the invention thus has the following advantages in the various embodiments:

Increase in usable storage volume by about 10%

Avoiding emissions from overpressure under the floating cover

Avoiding emissions when emptying the containers below the support height of the floating cover

Elimination of costly and time-consuming degassing of the spaces under the floating cover before inspection and repair measures at the storage tank

For a full understanding of the present invention, reference should now be made to the following detailed description of the preferred embodiments of the invention as illustrated in the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a vertical round container in the form of an open floating roof tank with a floating cover and a vapor line, which is guided on a piling tube, in the form of a bellows which is connected to a vapor equalization container.

FIG. 2 is a cross-sectional view of a further vertical round container also in the form of an open floating roof tank with a floating cover and vapor line in the form of a hose that is run along a rolling ladder.

FIG. 3 is a cross-sectional view of a vertical round container according to FIG. 1, with an additional fixed roof, and an inner floating cover in steel-pan construction.

FIG. 4 is a cross-sectional view of a vertical round container according to FIG. 3, wherein the floating cover is designed as a lightweight structural member construction with a vapor space between the liquid surface and the covering sheet skin.

FIG. 5 is a schematic representation of a storage facility with three storage containers, a vapor equalization container assigned to these storage containers, and a gas utilization/gas combustion device.

FIG. 6 is a schematic representation of a storage facility with storage containers grouped into two groups, each of which is assigned a vapor equalization container, which is connected to one another via a vapor equalization line and a pressure-increasing blower.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The preferred embodiments of the present invention will now be described with reference to FIGS. 1-6 of the drawings. Identical elements in the various figures are designated with the same reference numerals.

The round container, which is illustrated in a cross-sectional view in FIG. 1 and is designated by the reference sign 1, constitutes an open floating roof tank and comprises a container base 2 and a vertical container wall 3. The liquid (highly volatile hydrocarbons) located in the container space 4 is covered by a floating cover 5.

The floating cover 5 is supported by a ring pontoon 6 above the liquid, which is arranged around the peripheral area of the floating cover 5. The annular space 8 remaining between the outer wall 7 of the floating cover 5 and the inner side of the container wall 3 is closed by flexible sealing elements 9, such that, on the one hand, no precipitation water can penetrate into the space below the floating cover 5, and on the other hand no vapors from the space below the floating cover 5 can escape, wherein such vapors also accumulate in the annular space 8 above the liquid surface 10, as indicated in the figure.

A plurality of supports 11 with which the floating cover 5 rests on the container base 2 when the storage liquid is emptied from the container 1 to a residual volume is located on the underside of the floating cover 5 distributed over its surface. After the still remaining liquid is completely emptied out of the container 1 and the space 4 between the container bottom 2 and the floating cover 5 is degassed, the floating cover can also be inspected and maintained at the underside.

Located in the floating cover 5 is on the one hand a fitting in the form of an overpressure valve 12 for the autonomous checking of an overpressure in the container space 4 and on the other hand a fitting in the form of a vacuum safety valve 13 for the autonomous checking of a vacuum in the container space 4. Both fittings 12, 13 are connected via a vapor line 14 to a vapor equalization container 15 outside the round container 1.

The vapor line 14 comprises, within the container space, a vertically extending section, which is designed as a bellows 16. This bellows 16 lengthens or shortens depending on the floating height of the floating cover 5, as is indicated in the lower part of the bellows 16. In the embodiment shown in FIG. 1, the bellows 16 surrounds a fixed support 17, which is connected to the container wall 3 by means of brackets 18 at its lower end and at its upper end. This support 17 is additionally designed as a sampling, sounding and measuring tube, for which purpose it is provided in the longitudinal direction with a series of uniformly spaced holes 19, which guarantee that the leveling in the measuring tube results in the correct values. The end of the bellows 16 is attached to an expanded housing part 20 a of the jacket tube 20 for the measuring tube passage.

The vapor equalization container 15 comprises a flexible diaphragm 21 with a ballast weight 22 acting thereon, which produces the pressure in the equalization space 23.

Taking into account the flow resistances of the vapor line 14, the vapor equalization container 15 with its ballast weight 22 is designed to prevent a vacuum in the space 4 below the cover 5 by supplying vapors in the required amount and time to this space 4, and is also designed to prevent a pre-specified overpressure in this space 4 below the cover 5 by absorbing vapors in the required space and time from the space 4. The necessary pressure equalization is ensured by the pressure relief valve 12 and the vacuum valve 13.

FIG. 1 shows that the vacuum valve 13 has an actuating rod 24, which is longer than the length of the supports 11 so that the end of this actuating rod 24 comes into contact with the container bottom 2 of the round container 1 before the floating cover 5 rests at the bottom with the supports 11.

As a result, the vacuum valve 13 is actuated via the actuating rod 24 before the floating cover 5 rests on the container bottom 2 with the supports 11; this ensures the vapor supply from the vapor equalization container.

In order to also vent the annular space 8 between the outer wall 7 of the floating cover 5 and the container wall 3, which is sealed to the atmosphere by the flexible sealing elements 9, in the event of an excess of vapors, or the avoid a vacuum situation during container emptying, this annular space 8 is connected to the container space 4 via at least one further vapor line 25.

it is to be pointed out that, in the following description of the various exemplary embodiments, as shown in the figures, not all components are described again to an embodiment when they are described or explained with reference to another embodiment. Accordingly, the description of the various components of one embodiment may be applied to the respective components of another embodiment without explicitly mentioning this. Individual elements of an embodiment can also be transferred to another embodiment or used there.

In contrast to FIG. 1, FIG. 2 shows a further cross-section of a vertical round container I, which in its essential configuration corresponds to the round container 1 of FIG. 1. However, in FIG. 2 the vapor line 14 is run along a rolling ladder 27. The rolling ladder 27 is pivotally mounted on a bracket, designated with 18′, and rolls with its free lower end by means of rollers 27′ on a guide track 26 that rests on the floating cover 5 so that the rolling ladder 27 can move along the guide track 26 when the floating height of the floating cover 5 changes. The vapor line 14, which in this embodiment is designed as a flexible hose, thus runs at the rolling ladder 27. Such a rolling ladder 27 is typically present at containers without a fixed roof so that this rolling ladder 27 is used as a guide element for the vapor line 14.

FIG. 3 shows an embodiment, which is comparable to that of FIG. 1; however, the round container 1 is equipped with an additional fixed roof 8. By means of this fixed roof 8, the interior of the round container 1 and thus also the floating cover 5 is protected against rainwater so that the floating cover 5 does not have to bear any precipitates and does not need a ring pontoon. The construction of the vapor line 14 with the vertical section designed as a bellows 16, which surrounds the fixed support 17 serving as the direction-finding tube 17, is identical to the arrangement of FIG. 1.

The vertical round container 1 of FIG. 4 shown in a cross-sectional view corresponds to that of FIG. 3, whereby, however, the floating cover 5 is designed as a lightweight structural member construction. This embodiment is used when an inner floating cover is to be subsequently integrated into a closed container through the manhole in the jacket.

Storage facilities usually have a plurality of round containers 1 as shown in FIGS. 1 to 4. FIG. 5 shows, by way of example, a schematic representation of a storage facility with three storage containers, the upper storage container being one with a fixed roof and with a floating cover 5 b in lightweight construction corresponding to FIG. 4, the middle storage container being one with a fixed roof and a pan-type cover corresponding to FIG. 3, while the bottom storage container is an open storage container with a floating cover, a so-called floating roof tank, corresponding to FIG. 1. The respective vapor lines 14, which are assigned to the individual storage containers, are connected to the equalization space 23 of a common vapor equalization container 15. A pressure-increasing blower 29 is inserted into one of the vapor lines 14, which is assigned to the uppermost storage container with a cover 5 b in lightweight construction. This is required since the floating cover 5 b in lightweight construction cannot exert the necessary gas pressure for pressing vapors from the space 4 autonomously into the gas space 23 of the vapor equalization container 15. In the event of a negative pressure in the storage space 4 when the storage container is emptied, the vapors from the vapor equalization container 15 return autonomously into the gas chamber 4 when the valves 30 are closed and the valve 32 is open in the bypass line 31.

The shut-off valves 33 are always open during normal operation of the storage facility and are required only if one of the storage containers is to be separated from the rest of the storage system for operational reasons. The volume of the equalization space 23 of the vapor equalization container 15 can be increased or decreased in a suitable manner by the flexible diaphragm 21, wherein the pressure in the vapor line 14 corresponds to the pressure adjusted via the ballast weight 22 in the equalization space 23.

If the volume of the equalization space 23 of the vapor equalization container 15 is not sufficient to accommodate the vapors discharged from the storage containers, a gas recovery/gas combustion device 34 connected to the vapor equalization container 5 can be provided for further utilization or combustion of the gasses.

FIG. 6 shows a schematic representation of a further storage facility, which shows by way of example four storage containers, which are, grouped into two groups, each with two storage containers. Assigned to each group of two storage containers is a vapor-equalization container 15 a, 15 b, which are connected to their vapor lines 14. In order to make use of the volumes of the two vapor equalization containers 15 a, 15 b for both groups of storage containers when required, they are connected to one another via a vapor equalization line 35, into which a pressure increasing blower 29 with an associated bypass line 31 and the shut-off valves 30 and the further shut-off valve 32 is inserted, similar to the arrangement of FIG. 5, which is assigned to the upper storage container. Via this pressure-increasing blower 29, vapors are supplied from the low-pressure vapor equalization container 15 a to the higher-pressure vapor equalization container 15 b according to the requirements. In this way, the gas pressures in the vapor equalization containers 15 a and 15 b can be adapted to the possible gas pressures in the gas spaces 4 of the storage containers with different dead weights of the respective floating covers 5, 5 a, 5 b, 5 c, so that the required exchange of product vapors can occur autonomously and without risks for the respective storage container and floating covers.

FIG. 6 shows a further construction of a lightweight floating cover in the container 1 b. It is a floating cover made of GRP, with a surface weight of 150-200 N/m² (15-20 Kp/m²). All the floating covers shown in FIG. 6 have a different surface weight, which results in the different dimensions for the gas pressures in the vapor storage containers 15 a and 15 b.

The floating roof in the container 1 can have a surface weight of between 600 and 1000 N/m² (60 and 100 Kp/m²). The interior floating cover in the container 1 a may have surface weights of between 400 and 600 N/m² (40 and 60 Kp/m²). The lightweight floating aluminum cover in the container 1 c has only a surface weight of less than 100 N/m²(10 Kp/m²) and therefore cannot generate a high gas pressure under the floating cover. In the construction of FIG. 6, it is sufficient to assign a gas utilization/gas combustion device 34 to only one of the two vapor equalization containers 15.

FIG. 6 shows a suitable purging liquid container from which, after emptying of a storage container 1, 1 a, 1 b, 1 c a suitable purging liquid (water, heating oil, diesel, middle distillate, slop, etc.) is pumped into the space 4 under the floating cover 5, 5 a, 5 b, 5 c, wherein the vapors located in the space 4 are pressed into a vapor-equalization container 15, 15 a. Thereafter, the valve 33 is closed and the venting valve 41 at the outlet of the container is opened, and the purging liquid is pumped back into the purging liquid container 36. A pump 37, bypass lines 38 and valves 39 and 40 are shown with the reference signs 37, 38, 39 and 40, with which the purging liquid can be conveyed in different directions through corresponding switching of the valves. When the valves 39 are opened and the valves 40 are closed, the purging liquid is conveyed to the storage container 1, 1 a, 1 b, 1 c, and when the valves 40 are opened and the valves 39 are closed, the purging liquid is returned to the purging liquid container. The purging operation of the spaces 4 under the floating cover 5, 5 a, 5 b, 5 c saves the storage operator the costly and time-consuming removal of combustible and harmful vapors from the spaces 4 prior to inspections and repairs in the spaces 4 under the floating cover.

There has thus been shown and described a novel storage facility for the storage of highly volatile hydrocarbons which fulfills all the objects and advantages sought therefor. Many changes, modifications, variations and other uses and applications of the subject invention will, however, become apparent to those skilled in the art after considering this specification and the accompanying drawings which disclose the preferred embodiments thereof. All such changes, modifications, variations and other uses and applications which do not depart from the spirit and scope of the invention are deemed to be covered by the invention, which is to be limited only by the claims which follow. 

What is claimed is:
 1. A storage facility for the storage of highly volatile hydrocarbons, comprising at least one vertical round container which is provided with a floating cover for covering a liquid surface in the form of a floating roof or a floating cover, wherein an annular space formed between the cover and the container wall is sealed by means of flexible sealing elements and wherein fittings are integrated in the cover for the autonomous control of overpressure and negative pressure in a space underneath the cover, the improvement wherein the fittings of the at least one round container are connected to a vapor line which is led out of the container at an upper end and, in turn, is connected to a separate vapor equalization container with the round container and the vapor equalization container forming a closed system.
 2. A storage facility as in claim 1, wherein the vapor line has a vertically extending section inside the round container, which is formed as a bellows and which expands or contracts depending on a floating height of a floating cover.
 3. A storage facility as in claim 2, wherein the bellows surrounds a fixed support and wherein the bellows is attached at an upper end of the support.
 4. A storage facility as in claim 3, wherein the support is formed as at least one of a sampling, sounding, measuring and guide tube and as a roof support.
 5. A storage facility as in claim 1, wherein the vapor line is guided within the round container along a rolling ladder.
 6. A storage facility as in claim 1, wherein the vapor equalization container contains a flexible diaphragm with a ballast weight acting thereon.
 7. A storage facility as in claim 1, further comprising at least one of vapor recovery and vapor combustion devices connected to the vapor equalization container (15).
 8. A storage facility as in claim 1, comprising a plurality of storage containers, all connected to a common vapor equalization container.
 9. A storage facility as in claim 6, wherein the vapor equalization container is formed with its ballast weight, taking into account flow resistances of the vapor line such that it avoids a negative pressure in a space below the cover by supplying vapors to said space in the required quantity and time, and is operative to prevent a predetermined overpressure in said space below said cover by absorbing vapors in the required quantity and time from the space.
 10. Storage facility as in claim 1, further comprising a blower, arranged in the vapor line, which supports the removal of vapors to the vapor equalization container, and is controlled by pressure sensors in the container below the floating cover.
 11. A storage facility as in claim 1, comprising a plurality of storage containers which are divided into at least two groups according to their pressure exerted on the liquid therein via the floating cover, wherein a vapor equalization container is assigned to each group adapted to this pressure and wherein the different vapor equalization containers are connected via a vapor equalization line, into which a pressure increasing blower is inserted for conveying vapors from a low-pressure vapor equalization container to a higher pressure vapor equalization container.
 12. A storage facility as in claim 1, wherein a space remaining between the floating cover and the container bottom in the lowest position of the floating cover of the round container is connected to a purging liquid container, and wherein the hydrocarbon vapors present in said remaining space after the container has been emptied are removed to the vapor equalization container by introducing a purging liquid into said remaining space.
 13. A storage facility as in claim 12, wherein water or storage liquids with a low vapor pressure from other storage containers of the storage facility are used as purging liquid. 